Electrostatic latent image development apparatus

ABSTRACT

Apparatus for effecting development of an electrostatic latent image comprising a plurality of magnetic developing rollers positioned with intersecting magnetic force fields for effecting a blanket of developing material extending about and between the developing rollers adjacent an electrostatic latent image-bearing surface. A cylindrical roller, which may be electrically biased, is positioned between the magnetic developing rollers adjacent the electrostatic latent image bearing surface to enhance image development.

United States Patent 1151 sesame Young et al. Feb. 1, 1972 [54]ELECTROSTATIC LATENT IMAGE OTHER PUBLICATIONS DEVELOPMENT APPARATUSMedley, H. C. Development of Electrostatic Images. IBM

[72] Inventors: Eugene E Young Henrietta; Ryland Technical DisclosureBulletin,Augustl959, Vol. 2,No.2.

Rogers Webster both of Primary Examiner-Mervin Stein [73] Assignee:Xerox Corporation, Rochester, NY. Assistant Examiner-Leo Millstein AnDonldF.Dl ,Ja J.Rlbt dT .l. 221 Filed: Sept. 3, 1969 333, a a ey ms 3 aa e 21 A l. N 855 002 I 1 PP 0 1 57 ABSTRACT Apparatus for effectingdevelopment of an electrostatic latent [52] U.S.Cl ..lI8/637, l17/l7.5image comprising a plurality of magnetic developing rollers [51 Int. Cl...G03g 13/00 positioned with intersecting magnetic force fields foremicting [58] Field 0 Search ..l 623, 637; 1 17/1 a blanket ofdeveloping material extending about and betwcen the developing rollersadjacent an electrostatic latent image- [56] References Cited bearingsurface. A cylindrical roller, which may be electrically biased, ispositioned between the magnetic developing rollers UNITED STATES PATENTSadjacent the electrostatic latent image bearing surface to h d l t. 3,1l7,89l 1/1964 Lehmann ..1 18/637 en 'mage eve pmen 3,133,834 5/1964Sowiak ..1 18/637 12 Claims, 3 Drawing Figures ELECTROSTATIC LATENTIMAGE DEVELOPMENT APPARATUS BACKGROUND OF THE INVENTION This inventionrelates to the development of electrostatic latent images and, inparticular, to an apparatus for developing electrostatic latent imagesutilizing a magnetizable carrier material and an electroscopic tonerpowder.

More specifically, this invention relates to a magnetic brushdevelopment apparatus having an extended development zone.

In the method of development of electrostatic latent images by theapplication of electroscopic toner powder (for example, of the typedisclosed in Carlson US. Pat. No. 2,940,934) through the use of amagnetizable carrier material, referred to in the art as magnetic brushdevelopment, there is generally employed a single-magnetic brush closelyspaced adjacent a surface carrying latent electrical charges in imageconfiguration. As the electrostatographic art has progressed, the timein which the latent image is in contact with the development system hasdecreased because of the increased linear speed of the latentimage-bearing surface. Therefore, many attempts have been made toincrease the length of this development zone. However, due to spaceconstraints required of a commercial reproducing apparatus the additionof a plurality of development units has not been effective to solve thisproblem. One attempt to increase the effective length of the developmentzone without adding to the size of the development unit has been bypositioning two magnetic brush developing rollers adjacent each otherand adjacent an electrostatic latent image-bearing surface such that themagnetic fields emitted from the development rollers intersect to conveydeveloper material across the space between the rollers and in contactwith the latent electrical charges on the imagebearing surface. Whilesuch a system provides an increased effective development zone and hasproven to be very successful, it has been found in certain applicationswherein the magnetizable carrier material is of a certain size, that theweight of the developer material is such that gravitational forcesovercome the magnetic field emitted from the developing rollers andsufficient contact is not maintained between the developer material andthe electrostatic latent image-bearing surface throughout the entiredevelopment zone as is desired.

SUMMARY OF THE INVENTION Therefore, it is an object of this invention toimprove apparatus for developing electrostatic latent images.

Another object of this invention is to increase the effectivedevelopment zone of developing apparatus. A further object of thisinvention is to insure complete contact of developer material with anelectrostatic latent imagebearing surface the development of which iseffected by a plurality of magnetic brush development rollers positionedadjacent one another and the electrostatic latent image-bearing surfacesuch that their magnetic fields intersect to convey developer materialacross the space therebetween in contact with the latent image-bearingsurface.

These and other objects are attained in accordance with the presentinvention wherein there is provided a plurality of magnetic brushdeveloping units positioned adjacent each other and an electrostaticlatent image-bearing surface and including a rotatable cylindricalmember positioned between the developing units and the latentimage-bearing surface to effect image development throughout theextended developing zone.

Further objects of this invention, together with additional featurescontributing thereto and advantages accruing therefrom, will be apparentfrom the following description of one embodiment of the invention whenread in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a mechanical schematic of anautomatic xerographic reproducing machine utilizing the invention ofthis application;

FIG. 2 is a front perspective view of the developing apparatus to betterillustrate the developing units and the cylindrical roller whichenhances development of the electrostatic latent image throughout theextended developing zone; and

FIG. 3 is a schematic section of the apparatus shown in FIG. 2 takenalong lines 3-3.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, there isillustrated a cross section mechanical schematic of an automaticxerographic reproducing machine utilizing this invention. As in allelectrostatographic systems, illustrated by the xerographic reproducingmachine shown, a light image of a document to be reproduced is projected3 onto a photosensitive surface 1 to form an electrostatic latent imagethereon. Thereafter, the latent image is developed 4 to form anelectroscopic toner powder image in the configuration of the latentimage on the photoreceptor surface. The powder image may then betransferred 5 to a support material to which it may be permanently fixedas by heat fusing, or the toner powder may be permanently affixed to thephotoreceptive surface depending on the method of electrostatographicimaging employed as is well known in the art.

Referring now to FIGS. 2 and 3, the developing apparatus 50 extends thewidth of the photoreceptor l and is substantially enclosed except for anopening adjacent the photoreceptor whereat development of the latentelectrostatic image is effected, and an opening 11 upon which a tonerpowder dispenser 10 is positioned to replenish the toner depleted fromthe developer mixture during development of the electrostatic images.Within the housing of the developer apparatus there is a sump 51 at thelowermost portion of the housing containing developer materialcomprising magnetizable carrier material and colored electroscopic tonerparticles. The toner particles are many times smaller than the carriermaterial and, due to a triboelectric relationship therebetween,substantially uniformly coat the carrier material.

The developing apparatus 50 is positioned within the automaticxerographic reproducing machine adjacent to the photoreceptor l bysuitable brackets and braces appropriately secured to the developingapparatus and the frames of the machine. A suitable mounting 12 isprovided on the top of the developing apparatus between cover plates 52and 53 to position and retain the toner powder dispenser 10.

Development of the electrostatic latent image is effected by a blanketof developing material formed between a pair of adjacent magneticrollers 70 and positioned such that their magnetic force fieldsintersect to effect formation of a blanket of developing material uponthe rollers 70 and 80, and in the space therebetween adjacent thephotoreceptor l. The magnetic rollers 70 and 80 comprise outer cylinders'71 and 81, respectively, of a nonmagnetic material, such as aluminum,extending the width of the developer housing with elongated bar magnets72 and 82, respectively, extending nearly the full length of eachcylinder. The bar magnets 72 and 82 are each supported, for example, ona ferromagnetic bar 73 having rod 74 secured to each end, as by welding,and securely fastened in mounting blocks 75 appropriately secured toside frame plates 54 of the developer apparatus. The outer cylinders 71and 81 of nonmagnetic material are each mounted for rotation within thedeveloper housing by means of suitable bearing sur faces 76 carried bythe side frame plates 54 of the developer housing (FIG. 2). One end ofthe cylinder is enclosed by a cap 77 having a central opening therein,through which the rod portion 74 passes, and is rotatably supportedthereabout in the frame plate 54 by the bearing 76. The driven end isenclosed by an end cap 78 rotatably supported in suitable bearings inthe side frame plate 54 and having a drive gear 89 secured thereto toeffect rotation of each cylinder. The rotational drive for all otherrotary components of the developing apparatus 50 is derived from drivegear 89 by means of a suitable timing belt (not shown) engaging suitabledrive connections on each component. In this manner the outer cylindersmay be rotatably driven about the stationary elongated bar magnets 72and 82. The polar orientation of the elongated bar magnets is arrangedsuch that the magnetic force fields project through the walls of thenonmagnetic cylinders 71 and 111 to form the magnetizable carriermaterial into a brushlike configuration in a manner well known in theart.

As best shown in FIGS. 2 and 3, the peripheral walls of the cylinders 71and 81 are positioned in closely spaced relationship adjacent to oneanother. During a development cycle when both cylinders are rotating insynchronism about their respective stationary bar magnets 72 and 82, thebrush bristles produced by action of the magnetic field emanating fromthe magnets acting upon the magnetizable carrier material will form onthe upper region of the cylinder 71 within the magnetic field emanatingfrom magnets 72 and the under surface of the electrostatic image-bearingphotoreceptor 1. These bristles are formed during the developing cycle,and are produced by the magnetic field from the bar magnets 72. When thebristles are moved by the cylinder 71 out of the influence of magnet 72beyond the closest distance between the photoreceptor ll and thecylinder 71, they are attracted by the greater magnetic field of themagnet 82 which is stronger at this point than the diminished strengthof the magnetic field attributed to the magnet 72. The developermaterial is carried therealong during rotation of the cylinder 81 untilthe material reaches a point beyond the development zone whereat themagnet field is diminished and the carrier material and toner particlesdrop off the cylinder 81 and back into the sump portion 51 of thedeveloper apparatus. A suitable stripping mechanism such as anonmagnetizable doctor blade 96 may be utilized to insure that themagnetizable developer material is removed from the cylinder 81.

During movement of the developer material through the development zonebetween the two cylinders 71 and 81, the magnetizable developer materialis in the form of a blanket extending the entire distance (P16. 3)between the two cylinders and in contact with the photoreceptor 1.Therefore, the width of the development zone is larger than the sum ofthe individual development zones for either of the magnetic rollers 71or 81.

In order to insure that the blanket of developer material contacts theelectrostatic latent image-bearing surface throughout the extendeddevelopment zone, a rotatable wire brush or other cylinder 60 ispositioned between the magnetic developing rollers 70 and 80, adjacentthe latent image-bearing surface 1. The cylinder 60 is rotatablysupported in suitable bearing surfaces carried by side frame plates 54and may be positively driven, or act as an idler, and functions tosupport the developer material as it passes from cylinder 71 to cylinder81. The cylinder 60 prevents the developer tufts from collapsing undertheir own weight as they pass from the magnetic field emanating fromroller 70 into the magnetic field emanating from roller 80. In additionto the cylinder 60 supporting the developer material in brushlike tuftsadjacent the latent image-bearing surface, by applying a suitableelectrical bias, such as 250 volts, to the cylinder a developmentelectrode effect will occur to further enhance image development.

After the developer material has effected development of the latentimage on the photoreceptor surface, the material is removed from thecylinder 81 and passed to the sump portion 51 of the developerapparatus. A developer conveyor 20 is rotatably mounted within the sideframe plates 541 of the developer apparatus by suitable bearings andcarries the developer material from the sump portion to be introduced tothe magnetic developing rollers 70 and 80. The developer conveyorcomprises a plurality of spaced buckets 21 carried by a belt 22appropriately driven by a shaft 23 rotatably mounted in suitable bearingsurfaces in the side frame plates d and driven by means ofa gear (notshown) suitably secured to one end of the shaft 23 and engaging asuitable drive system.

While there has been shown and described one embodiment of theinvention, it is intended that the invention be not limited to the exactform shown and described or to anything less than the whole of theinvention as set forth in the appended claims.

What is claimed is:

1. Apparatus for developing a support surface carrying latent electricalcharges selectively retained in image configa ration including a firstmagnetic field emitting means to convey a quantity of magnetizabledeveloper material in contact with a sup port surface to be developed,

a second magnetic field emitting means spaced therefrom with therespective magnetic fields intersecting to convey developer materialacross the space therebetween in con tact with the latent electricalcharges to effect the development thereof, and

means positioned between said first and second magnetic field emittingmeans to support developer material conveyed across the spacetherebetween in contact with the support surface.

2. Apparatus for developing a support surface having latent electricalcharges selectively retained in image configuration including a firstmagnetic field emitting means to move a quantity of magnetizabledeveloper material in contact with a support surface having latentelectrical charges selectively retained in image configuration,

a second magnetic field emitting means spaced therefrom with therespective emitted magnetic fields intersecting to move magnetizabledeveloper material in contact with the support surface through the spacebetween said first and second magnetic field emitting means to effectthe development of the latent electrical charges selectively retained inimage configuration, and

means positioned between said first and second magnetic field emittingmeans to support developer material in contact with the support surfaceas the developer material is moved between said magnetic field emittingmeans in response to the intersecting of their respective magneticfields.

3. Apparatus for developing a support surface having latent electricalcharges selectively retained in image configuration including aplurality of spaced cylinders rotatably supported adjacent a supportsurface having latent electrical charges tively retained in imageconfiguration to convey a quantity of magnetizable developer materialthereto for ing the development thereof,

magnetic field producing means supported within each of said cylindersto emit a magnetic field passing therethrough and intersecting with themagnetic field emitted from within another of said spaced cylinders,

means to rotate said cylinders to convey a magnetizable developermaterial into contact with the support surface and across the spacebetween said cylinders in response to said intersecting magnetic fieldsfor effecting the development of the latent image on the supportsurface, and

means positioned between said plurality of spaced cylinders adjacent thesupport surface to support the magnetizable developer material inbrushlike tufts in response to the magnetic fields emitted through saidcylinders.

ll. The apparatus of claim 3 wherein said means to support themagnetizable developer material in brushlike tufts in response to themagnetic field emitted through said cylinders includes a rotatablecylinder supported adjacent the latent image bearing support surfacewith the magnetizable developer material passing therebetween.

5. Apparatus for developing a support surface having latent electricalcharges selectively retained in image configuration including,

a plurality of spaced cylinders rotatably supported adjacent a supportsurface having latent electrical charges selectively retained in imageconfiguration to convey a quanti ty of magnetizable developer materialthereto for effecting the development thereof.

magnetic field producing means supported within each of said cylindersto emit a magnetic field passing therethrough and intersecting with themagnetic field emitted from within another of said spaced cylinders,

means to rotate said cylinders to convey a magnetizable developermaterial into contact with the support surface and across the spacebetween said cylinders in response to said intersecting magnetic fieldsfor effecting the development of the latent image on the supportsurface, and

an electrically conductive rotatable cylinder supported adjacent thelatent image-bearing support surface between adjacent pairs of saidspaced cylinders to support the magnetizable developer material inbrushlike tufts in response to the magnetic fields emitted through saidcylinders.

6. The apparatus of claim 5 wherein said electrically conductivecylinder is electrically biased to a potential of approximately 250volts.

7. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising,

a first magnetic field emitting means for conveying a quantity ofmagnetizable developer material over the support surface to bedeveloped,

a second magnetic field emitting means for conveying a quantity ofmagnetizable developer material from said first magnetic field emittingmeans over the support surface to be developed, said second magneticfield emitting means being spaced from said first magnetic fieldemitting means such that the respective magnetic fields are inoverlapping relationship with each other, and

means positioned between said first magnetic field emitting means andsaid second magnetic field emitting means for supporting developermaterial conveyed from said first magnetic field emitting means to saidsecond magnetic field emitting means in contact with the support surfaceto be developed.

8. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising,

a first magnetic field emitting means for moving a quantity ofmagnetizable developer material over the support surface to bedeveloped,

a second magnetic field emitting means for moving a quantity ofmagnetizable developer material over the support surface to bedeveloped, said second magnetic field emitting means being spaced fromsaid first magnetic field emitting means with the respectively emittedmagnetic fields intersecting therebetween to support magnetizabledeveloper material across the space between said first and said secondmagnetic field emitting means, and

means positioned between said first and said second magnetic fieldemitting means for supporting developer material in contact with thesupport surface to be developed as the developer material is transportedfrom said first magnetic field emitting means to said second magneticfield emitting means.

9. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising,

a first cylindrical member supported for rotation adjacent a supportsurface having latent electrostatic charge patterns thereon which are tobe developed,

a first magnetic field producing means supported within said firstcylindrical member for attracting a quantity of magnetizable developermaterial to the surface of said cylindrical member for movement of saidcylindrical member over said support surface,

a second cylindrical member supported for rotation adjacent said supportsurface and spaced from said first cylindrical member,

a second magnetic field producing means supported within said secondcylindrical member, the field from said second magnetic field producingmeans extending across the space between said first and said secondcylindrical members into the field of said first magnetic fieldproducing means to attract a quantity of magnetizable developer materialfrom the surface of said first cylindrical member to the surface of saidsecond cylindrical member for movement by said second cylindrical memberover said support surface, and

means positioned between said first and said second cylin drical membersfor supporting the magnetizable developer material proximate to thesupport surface as the developer material is moved across the spacebetween said first and said second cylindrical members.

10. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising,

a first cylindrical member supported for rotation adjacent a supportsurface having latent electrostatic charge patterns thereon which are tobe developed,

a first magnetic field producing means supported within said firstcylindrical member for attracting a quantity of magnetizable developermaterial to the surface of said cylindrical member for movement by saidcylindrical member over said support surface,

a second cylindrical member supported for rotation adjacent said supportsurface and spaced from said first cylindrical member,

a second magnetic field producing means supported within said secondcylindrical member, the field from said second magnetic field producingmeans extending across the space between said first and said secondcylindrical members into the field of said first magnetic fieldproducing means to attract a quantity of magnetizable developer materialfrom the surface of said first cylindrical member to the surface of saidsecond cylindrical member for movement by said second cylindrical memberover said support surface, and

a support member of generally cylindrical configuration positionedintermediate said first and said second cylindrical members and adaptedfor rotation to support the magnetizable developer material proximate tothe support surface as the developer material is moved across the spacebetween said first and said second cylindrical members.

11. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising,

a plurality of cylindrical members supported in spaced relationship toeach other adjacent said support surface for moving magnetizabledeveloper material over said support surface,

magnetic field producing means supported within said cylindricalmembers, the respective fields from said magnetic field producing meansextending across the spaces between adjacent ones of said cylindricalmembers in overlapping relationship to attract magnetizable developermaterial from the surfaces of precedingly adjacent cylindrical membersto the surfaces of succeedingly adjacent cylindrical members as thedeveloper material is moved by said cylindrical members over saidsupport surface, and

means positioned between adjacent pairs of said cylindrical members forsupporting the magnetizable developer material proximate to the supportsurface as the developer material is moved across the spaces betweensaid cylindrical members.

12. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising,

a plurality of generally cylindrical members supported in rotatablespaced relationship to each other adjacent said support surface formoving magnetizable developer material in brushlike tufts over saidsupport surface,

magnetic field producing means supported within said cylindricalmembers, the respective fields from said magnetic field producing meansextending across the spaces between adjacent ones of said cylindricalmembers in over said support surface, and means positioned betweenadjacent pairs of said cylindrical members for supporting themagnetizable developer material proximate to the support surface as the:developer material is moved across the spaces between said cylindricalmembers.

:x =1: *0: t n

1. Apparatus for developing a support surface carrying latent electricalcharges selectively retained in image configuration including a firstmagnetic field emitting means to convey a quantity of magnetizabledeveloper material in contact with a support surface to be developed, asecond magnetic field emitting means spaced therefrom with therespective magnetic fields intersecting to convey developer materialacross the space therebetween in contact with the latent electricalcharges to effect the development thereof, and means positioned betweensaid first and second magnetic field emitting means to support developermaterial conveyed across the space therebetween in contact with thesupport surface.
 2. Apparatus for developing a support surface havinglatent electrical charges selectively retained in image configurationincluding a first magnetic field emitting means to move a quantity ofmagnetizable developer material in contact with a support surface havinglatent electrical charges selectively retained in image configuration, asecond magnetic field emitting means spaced therefrom with therespective emitted magnetic fields intersecting to move magnetizabledeveloper material in contact with the support surface through the spacebetween said first and second magnetic field emitting means to effectthe development of the latent electrical charges selectively retained inimage configuration, and means positioned between said first and secondmagnetic field emitting means to support developer material in contactwith the support surface as the developer material is moved between saidmagnetic field emitting means in response to the intersecting of theirrespective magnetic fields.
 3. Apparatus for developing a supportsurface having latent electrical charges selectively retained in imageconfiguration including a plurality of spaced cylinders rotatablysupported adjacent a support surface having latent electrical chargesselectively retained in image configuration to convey a quantity ofmagnetizable developer material thereto for effecting the developmentthereof, magnetic field producing means supported within each of saidcylinders to emit a magnetic field passing therethrough and intersectingwith the magnetic field emitted from within another of saiD spacedcylinders, means to rotate said cylinders to convey a magnetizabledeveloper material into contact with the support surface and across thespace between said cylinders in response to said intersecting magneticfields for effecting the development of the latent image on the supportsurface, and means positioned between said plurality of spaced cylindersadjacent the support surface to support the magnetizable developermaterial in brushlike tufts in response to the magnetic fields emittedthrough said cylinders.
 4. The apparatus of claim 3 wherein said meansto support the magnetizable developer material in brushlike tufts inresponse to the magnetic field emitted through said cylinders includes arotatable cylinder supported adjacent the latent image bearing supportsurface with the magnetizable developer material passing therebetween.5. Apparatus for developing a support surface having latent electricalcharges selectively retained in image configuration including, aplurality of spaced cylinders rotatably supported adjacent a supportsurface having latent electrical charges selectively retained in imageconfiguration to convey a quantity of magnetizable developer materialthereto for effecting the development thereof, magnetic field producingmeans supported within each of said cylinders to emit a magnetic fieldpassing therethrough and intersecting with the magnetic field emittedfrom within another of said spaced cylinders, means to rotate saidcylinders to convey a magnetizable developer material into contact withthe support surface and across the space between said cylinders inresponse to said intersecting magnetic fields for effecting thedevelopment of the latent image on the support surface, and anelectrically conductive rotatable cylinder supported adjacent the latentimage-bearing support surface between adjacent pairs of said spacedcylinders to support the magnetizable developer material in brushliketufts in response to the magnetic fields emitted through said cylinders.6. The apparatus of claim 5 wherein said electrically conductivecylinder is electrically biased to a potential of approximately 250volts.
 7. Apparatus for developing latent electrostatic charge patternson a support surface comprising, a first magnetic field emitting meansfor conveying a quantity of magnetizable developer material over thesupport surface to be developed, a second magnetic field emitting meansfor conveying a quantity of magnetizable developer material from saidfirst magnetic field emitting means over the support surface to bedeveloped, said second magnetic field emitting means being spaced fromsaid first magnetic field emitting means such that the respectivemagnetic fields are in overlapping relationship with each other, andmeans positioned between said first magnetic field emitting means andsaid second magnetic field emitting means for supporting developermaterial conveyed from said first magnetic field emitting means to saidsecond magnetic field emitting means in contact with the support surfaceto be developed.
 8. Apparatus for developing latent electrostatic chargepatterns on a support surface comprising, a first magnetic fieldemitting means for moving a quantity of magnetizable developer materialover the support surface to be developed, a second magnetic fieldemitting means for moving a quantity of magnetizable developer materialover the support surface to be developed, said second magnetic fieldemitting means being spaced from said first magnetic field emittingmeans with the respectively emitted magnetic fields intersectingtherebetween to support magnetizable developer material across the spacebetween said first and said second magnetic field emitting means, andmeans positioned between said first and said second magnetic fieldemitting means for supporting developer material in contact with thesupport surface to be developed as the developer matErial is transportedfrom said first magnetic field emitting means to said second magneticfield emitting means.
 9. Apparatus for developing latent electrostaticcharge patterns on a support surface comprising, a first cylindricalmember supported for rotation adjacent a support surface having latentelectrostatic charge patterns thereon which are to be developed, a firstmagnetic field producing means supported within said first cylindricalmember for attracting a quantity of magnetizable developer material tothe surface of said cylindrical member for movement of said cylindricalmember over said support surface, a second cylindrical member supportedfor rotation adjacent said support surface and spaced from said firstcylindrical member, a second magnetic field producing means supportedwithin said second cylindrical member, the field from said secondmagnetic field producing means extending across the space between saidfirst and said second cylindrical members into the field of said firstmagnetic field producing means to attract a quantity of magnetizabledeveloper material from the surface of said first cylindrical member tothe surface of said second cylindrical member for movement by saidsecond cylindrical member over said support surface, and meanspositioned between said first and said second cylindrical members forsupporting the magnetizable developer material proximate to the supportsurface as the developer material is moved across the space between saidfirst and said second cylindrical members.
 10. Apparatus for developinglatent electrostatic charge patterns on a support surface comprising, afirst cylindrical member supported for rotation adjacent a supportsurface having latent electrostatic charge patterns thereon which are tobe developed, a first magnetic field producing means supported withinsaid first cylindrical member for attracting a quantity of magnetizabledeveloper material to the surface of said cylindrical member formovement by said cylindrical member over said support surface, a secondcylindrical member supported for rotation adjacent said support surfaceand spaced from said first cylindrical member, a second magnetic fieldproducing means supported within said second cylindrical member, thefield from said second magnetic field producing means extending acrossthe space between said first and said second cylindrical members intothe field of said first magnetic field producing means to attract aquantity of magnetizable developer material from the surface of saidfirst cylindrical member to the surface of said second cylindricalmember for movement by said second cylindrical member over said supportsurface, and a support member of generally cylindrical configurationpositioned intermediate said first and said second cylindrical membersand adapted for rotation to support the magnetizable developer materialproximate to the support surface as the developer material is movedacross the space between said first and said second cylindrical members.11. Apparatus for developing latent electrostatic charge patterns on asupport surface comprising, a plurality of cylindrical members supportedin spaced relationship to each other adjacent said support surface formoving magnetizable developer material over said support surface,magnetic field producing means supported within said cylindricalmembers, the respective fields from said magnetic field producing meansextending across the spaces between adjacent ones of said cylindricalmembers in overlapping relationship to attract magnetizable developermaterial from the surfaces of precedingly adjacent cylindrical membersto the surfaces of succeedingly adjacent cylindrical members as thedeveloper material is moved by said cylindrical members over saidsupport surface, and means positioned between adjacent pairs of saidcylindrical members for supporting the magnetizable developer materialproximate to the support surface as the developer material is movedacross the spaces between said cylindrical members.
 12. Apparatus fordeveloping latent electrostatic charge patterns on a support surfacecomprising, a plurality of generally cylindrical members supported inrotatable spaced relationship to each other adjacent said supportsurface for moving magnetizable developer material in brushlike tuftsover said support surface, magnetic field producing means supportedwithin said cylindrical members, the respective fields from saidmagnetic field producing means extending across the spaces betweenadjacent ones of said cylindrical members in overlapping relationship,said overlapping fields forming brushlike tufts of magnetizabledeveloper material on the surfaces of said cylindrical members andattracting the magnetizable developer material from the surfaces ofprecedingly adjacent cylindrical members to the surfaces of succeedinglyadjacent cylindrical members as the developer material is moved by saidcylindrical members over said support surface, and means positionedbetween adjacent pairs of said cylindrical members for supporting themagnetizable developer material proximate to the support surface as thedeveloper material is moved across the spaces between said cylindricalmembers.